Microfractionation still with capillary tube offtakes for condensate



Jan. 18, 1949. c w. GOULD, JR 2,459,375

MICROFRACTIO NATION STILL WITH CAPILLARY TUBE OFF TAKES FOR CONDENSATE Filed Sept. 15, 1944 INVENTOR. 6242K W Gouzw/e.

Patented Jan. 18, 1949 2,459,375 MICROFRACTIONATION STILL WITH CAPIL- LARY TUBE OFFTAKES FOR CONDENSATE Clark Webster Gould, Jr.,

Pasadena, Calif., as-

signor to California Institute Research Foundafor tlon, Pasadena, Calif., a

his

corporation of Call- Appllcatlon September 15, 1944, Serial No. 554,314

10 Claims. 1

This invention relates to microfractionation stills and the objects of this invention are:

First, to provide a microfracticnation still for the precise fractionation of extremely small liquid samples; for example. samples having volumes between 0.1 and 0.4 cubic centimeter, the distillate being collected in individual fractions as small as 0.005 cubic centimeter.

Second, to provide as a part of such still. a condenser and receiver system wherein contamination of any fraction by a preceding fraction is reduced to a minimum.

Third, to provide a microfractionation still which includes a receiving system wherein several fractions each less than 0.05 cc. in volume may be individually collected in succession during a distillation at reduced pressure so that the distillation may continue without interruptions necessitated by breaking the vacuum to remove single fractions from the still.

Fourth, to provide a microfractionation still which incorporates a novel and eflicient means for transferring the distillate from the condenser to the receiving cup in minute quantities and with minimum loss.

Fifth, to provide an essentially adiabatic fractionating column of high efliciency (the height equivalent to one theoretical plate being less than 15 mm.) and low liquid hold up (less than 0.04 cc.)

Sixth, to provide a microfractionation still which incorporates a simple arrangement for measuring vapor temperatures of the distillate by means of a thermocouple placed at the head of the column.

Seventh, to provide a microfractionation still which is inherently simple to use so that personnel familiar with the technique of fractional distillation upon usual laboratory scale may effect satisfactory separations.

With the above and other objects in view, as may appear hereinafter, reference is directed to the accompanying drawings in which:

Figure 1 is a partial sectional, partial elevational view of one form of the microfractionation still.

Figure 2 is an enlarged sectional view of the sample collecting cups and adjacent portions of the apparatus.

Figure 3 is a sectional view taken through 33 of Figure 2.

Figure 4 is a partial sectional, partial elevational view of a modified form of still wherein the fractionating column is omitted.

Figure 5 is a sectional view thereof taken through 5-5 of Figure 4.

With reference to the structure shown in Fisures 1, 2 and 3, the still includes a fractionating column I in the form of a small thin-walled vertically disposed glass tube, the lower end of 2 which is sealed to, and communicates with a boiler 2 in the form of a small glass bulb having, in the illustration, a capacity of approximately 0.4 cc.

The fractionating column I is enclosed by a jacket I which is internally silvered except for two vertical windows (not shown) in the front and back of the Jacket, through which the fractionating column may be viewed. The annular space between the fractionating column I and the jacket 3 is evacuated.

Within the fractionating column is a packing coil 4. The fractionating column I continues above the Jacket 3 to form a neck portion 5 and a stem 6. The stem 6 is adapted to receive a removable cap I, the stem and cap forming aground Joint. The cap I is provided with a thermocouple well 8 which extends into the neck I and upper end of the jacketed portion of the fractionating column.

A condenser shell 9, in the form of a tube, branches outward and downward from the neck 5 at approximately a thirty-five degree angle with the horizontal. The lower end of the condenser shell communicates with a collector chamber III in the form of a short tube of larger diameter than the condenser shell and open at its lower end. A vacuum line nipple II projects from one side of the collector chamber I0. A brace rod, I2 extends between the collector chamber I0 and the jacket 3.

The condenser shell 9 and upper end of the collector chamber I0 receive a condenser I3. The condenser comprises an outer tube I4 and an inner tube I5 which communicate respectively with an outlet nipple I6 and an inlet nipple I1. The condenser is substantially V-shaped, one leg of which extends within the condenser still 9 and is spaced from the walls thereof. The other leg thereof, protrudes laterally .and upward from the upper end of the collector chamber III, the outer tube being sealed to the walls of the chamber.

The extremities of the outer condenser tube It within the shell 0 is closed and the inner condenser tube IS terminates short of this end so that a cooling fluid may be passed into the condenser through the inner tube and return through the annular space between the inner and outer tubes.

At the apex of the V-shaped condenser there is provided a small depending lip I8, shown best in Figure 2. I

The lower or open end of the collector chamber is adapted to receive a cap I9 forming a ground fit therewith. Within the cap I! is an upstanding stem 20 which extends into the chamber I0 and supports several collector cups 2|. The collector cups are arranged parallel with each other.

In the illustration four such cups are shown,

merely a short length of glass tubing having approximately 'a 0.3 millimeter bore and placed loosely in the cup. The upper end of each cup is constricted or inturned to form a loose guide for the siphon and is preferably fire polished.

The axis of rotation of the cap I! is such that the capillary siphons may be brought successively into contact with the collector lip ID, as shown best in Figure 2 upon rotation of the cap. A heating coil 23 is wrapped around the jacket 3 and may be series connected with a heating coil 24 wrapped around the condenser shell 3. The heating coils are incorporated in a suitable electrical circuit, not shown.

The microfractionation still functions as follows:

The sample to be distilled is placed in the boiler 2 by means of a tube inserted through the fractionating column I, and the cap I replaced. The sample is then heated. The vapors pass upward through the fractionating column; part of the vapors condense upon the packing coil and the condensate returns to the boiler by descending the spiral packing coil. With proper control of the heat supplied to the boiler 2 and proper control of the current supplied to the heating coil 24, almost all of the vapors can be caused to condense in the short section of the column between the jacket and the entrance to the condenser shell. This total refluxing materially increases the effectiveness of the separation of moisture and more volatile impurities from the liquid to be distilled. When most of the volatile impurities are removed, as shown by a constant thermocouple reading, the heat applied to the boiler and/or current supplied to the heating coil 23 is slightly increased so as to cause the desired distillation rate, usually about 0.002 cc/min. The reflex ratio, 1. e. the amount of material returned to the column divided by the amount distilled, can thus be readily controlled.

Inasmuch as the condenser shell 3 is heated by the heating coil 23, all condensation takes place on the'outer tube of the condenser. As the distillate condenses it flows to the lower end of the condenser and collects on the lip l3 moistening the upper end of the capillary siphon 22. The distillate is then drawn, by capillary action, through the capillary siphon to the botton of the corresponding collector cup. The collector cups are used in succession to collect the different fractions which may be distilled from the sample. The number of cups provided depend upon the character of the sample, in most cases four cups are sufllcient.

The length of the capillary siphon and, therefore, the length of its collector cup should be less than the height the liquid would normally rise in the capillary tube, that is, if the distillate has a high surface tension and low specic gravity the siphon may be relatively long, whereas, if'the surface tension is low and specific gravity is high the siphon tube must be correspondingly shorter. For example, the siphons shown in Figure 2, have a length of about 1'7 mm. and a bore of 0.3 mm., and are excellent for collecting carbon tetrachloride, which has both a low surface tension and high specific gravity. Insofar as the various constituents of the sample have appreciably different boiling points, one fraction is completely condensed, collected, and the outer tube of the condenser becomes dry before the next fraction begins to collect. Thus, a very clean cut separation may be obtained.

Since the annular space between the condenser and its shell is about equal in area to that of the column itself, pressure gradients between the top of the volumn and the vacuum line are reduced to a minimum, thus allowing greater accuracy in the determination of boiling points at reduced pressure. Furthermore, this space is, at all times, open; that is, it is never closed by drops of liquid bridging between the condenser.

and shell. Also because the condensation takes place on the comparatively small outer surface of the outer condenser tube rather than the inner surface of a larger tube, very'small quantities of distillate may be caused to accumulate at the collector lip, in fact, it is possible to condense and collect a fraction having a volume of only 0.005 cc.

The construction shown in Figures 4 and 5 illustrates a simple molecular still. In this construction a condenser shell 3|, which may be a straight length of tube, mounted on an incline, is provided at its upper end with a depending protuberance forming a boiler 32. The lower end of the condenser shell is ground to receive a correspondingly ground portion of a condenser unit 33, comprising an outer tube 34 which extends concentrically within the condenser shell to a point near its upper end. Within the outer tube 34 is an inner condenser tube 35 terminating just short of the inner or upper end of the outer tube.

The condenser tubes 34 and 35 communicate with an outlet nipple 36 and an inlet nipple 31 so that a cooling liquid may flow into the condenser through the inner tube 35 and return through the annular space between the inner and outer tubes. At a suitable mid-point the outer tube 34 is provided with an annular collector lip or flange 38. The flange is so shaped that the distillate condensing on the upper end of outer tube 33 fiows downward to the flange without wetting the side of the flange facing the lower end of the condenser.

The condenser shell 3| is provided with a depending nipple 39 which forms a ground fit with the cap l9, described in connection with the structure shown in Figure 1.

The capillary siphons 22 are adapted to con tact the axially upward side of the flange 38 and draw ofi the distillate as described herein before. The condenser shell 3i is also provided with a vacuum line nipple 40.

As in the first described structure, the condenser shell 3| may be provided with a heating The various changes and alternate arrangements may be made within the scope of the appended claims.

I claim:

1. An apparatus for the microdistillation of liquids comprising: a boiler; a condenser shell communicating therewith; a condenser mounted within said shell and spaced from the walls thereof and having a condensing surface; a colliquids comprising: a boiler; a condenser shell moving each of said cups in' succession in'to position for contact of its capillary tube with said tip. 4. The combination with a micro'distillation device, of a distillate collecting means, comprising;

a condenser having an enclosedtubular condensing surface disposed so that liquids'drain downwardly thereon; a collector tip at a low point on a said condensing surface; a plurality of; cups arranged side by side; a capillary tube in} each cup engageable with said tip; and means for moving each of said cups in succession into positionior contact of its capillary tube with said tip.

' 5. An apparatus for the microdistillation of liquids comprising: a boiler; a condenser shell communicating with the boiler; a condenser unit mounted within said shell and including inner and outer tubes for the circulation of a cooling medium, the outer tube being spaced from from the walls of said shell and its outer surface forming a condensing surface; a tip on the outer tube of the condenser unit for receiving liquid as it condenses on said surface and drains downwardly thereon; a receiving cup positioned below said tip; and a capillary tube loosely positioned in said cup and adapted to contact said lip to transfer liquid from said tip to said cup.

6. An apparatus for the microdistillation of liquids comprising: a boiler; a condenser shell communicating with the boiler; a condenser unit mounted within said shell and including inner and outer tubes for the circulation of a cooling medium, 'the outer tube being spaced from the walls of said shell and its outer surface forming a condensing surface; a tip on the outer tube of the condenser unit for receiving liquid as it condenses on said surface and drains downwardly thereon; a plurality of liquid collecting cups; a capillary tube positioned in each cup and protruding therefrom; and a common supporting means for said cups for moving each of said cups in succession into position for engagement ofits capillary tube with said tip.

7. A microfractionating still comprising: a boiler; a fractionating column extending upwardly therefrom; a condenser shell communicating with the upper end of said column; a thermocouple well at the juncture of said column and shell; a condenser unit mounted within said shell and including inner and outer tubes for the circulation of a cooling medium, the outer tube being spaced from the walls of said shell and its outer surface forming a condensing surface; a lip on the outer tube of the condenser unit for receiving liquid as it condenses on said surface and drains downwardly thereon; a receiving cup positioned below said lip; and a capillary tube loosely positioned in said cup and adapted to contact said tip to transfer liquid from said lip to said cup.

8. A microfr'actionation still comprising: a boiler; a fractionating column extending upwardly therefrom; a condenser shell communicating with the upper end of said column; a thermocouple well at the juncture of said column and shell; a condenser unit mounted within said shell and including inner and outer tubes for the circulation of a cooling medium, the outer tube being spaced from the walls of said shell and its outer surface forming a condensing surface; a tip on the outer tube of the condenser unit for receiving liquid as it condenses on said surface and drains downwardly thereon; a plurality of liquid collecting cups; a capillary tube positioned in each cup and protruding therefrom; and a common supporting means for said cups for moving each 'of said cups in succession into position for engagement of its capillary tube with said tip.

9. A microfractionation still comprising: a boiler; a fractionating column extending upwardlytherefrom; a condenser shell communi- ,cating with the upper end of said column and sloping downwardly therefrom; a condenser unit positioned within said condenser shell and including an inner tube for inflow of a coolingmedium and an outer tube coveringsaid inner tube and defining therewith a passage for outflow of the cooling medium, said tube being bent in the form of an obtuse V, and a draining tip at the apex of the V; a collector chamber open at its lower end and communicating with said condenser shell below ,said tip; a closure for said chamber; and a collector cup supported by said closure; and a capillary tube in said cup and adapted to contact said tip.

10. A microfractlonation still comprising: a boiler; a fractionating column extending upwardly therefrom; a condenser shell communieating with the upper end of said column and sloping downwardly therefrom; a condenser unit positioned within said condenser shell and including an inner tube for inflow of a cooling medium and an outer tube covering said inner tube and defining therewith a passage for outflow of the cooling medium, said tube being bent in the form of an obtuse V, and a draining tip at the apex of the V; a collector chamber open at its lower end and communicating with said condenser shell below said tip; a closure member for the lower end of said chamber; a plurality of collector cups supported by said closure member; and a capillary tube in each cup, said closure member adapted to be turned to bring said capillary tubes in successive contact with said tip.

CLARK WEBSTER GOULD, JR.

REFERENCES CITED The following references are of record in the OTHER REFERENCES "A Fractional Distillation Microapparatus," by C. Tiedcke; Ind. & Eng. Chem., Anal. Ed., vol. 15, No. 1, pages 81-82, Jan. 15, 1943.

A Microdistillation Apparatus, by L. 0. Craig; Ind. & Eng. Chem., Anal. Ed., vol. 8, No. 3, May 15, 1936, pages 219, 220; also vol. 9, No.9, Sept. 15, 1937, pages 441,443, 442,

A Micro Distillation Apparatus, by S. A. Slviader et al.; Ind. 81 Eng. Chem, Anal. Ed., vol. 11. No. 1, Jan. 15, 1939, pages 54-55. 

